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Full text of "Handbook Of Chemical Engineering - I"

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294
CHEMICAL ENGINEERING
that it will be tightly wrapped on the canvas. A weight of wire of about 14 gage is suitable for winding the filtering medium. In the preparation of potash from Nebraska brines wire cloth has been substituted for the under cover of burlap.
Life of Filter Fabric.—For ordinary cold filtrations the filter fabric will last from 2 to 6 months or longer. With hot liquids which attack the fabric the cloth may only last this number of days. In cold Steffens house sugar work it may last from 21 to 50 days depending on the care of the cloth. In the cold work the saccharate of lime has a tendency to blind the pores of the filter cloth and it is necessary to scrub it with a weak solution of hydrochloric acid every 3 days and this necessary operation shortens the life of the filter cloth.
For most medium uses cotton fabrics give the best service. Wool and woven metal coth is also used. For ordinary cold work an 8 to 16-oz. duck or its equivalent in other cotton fabrics will show the best results. Other things being equal the more open the fabric the better the filtration results. If a little cloudiness in the filtrate is not objectionable it is better -to equip the filter with an open fabric, preferably of medium weight if the greatest possible capacity is desired.
The Portland filter is built in drum sizes of 6, 8, 12 and 14 ft. diameter and with various width of face up to 16 ft. The Oliver filter is built in the following sizes of filter drum:
Diameter          Length	Area, square feet	Diameter          Length	Area, square feet
3 ft. 0 in. by   0 ft. 6 in.	4	8 ft. 0 in. by 10 ft. 0 in.	250
3 ft. 0 in. by   1 ft. 0 in.	9	8 ft. 0 in. by 12 ft. 0 in.	300
3 ft. 0 in. by   2 ft. 0 in.	18	11 ft. 6 in. by   8 ft. 0 in.	288
3 ft. 0 in. by   4 ft. 0 in.	36	11 ft. 6 in. by 10 ft. 0 in.	360
4 ft. 0 in. by   2 ft. 0 in.	25	11 ft. 6 in. by 12 ft. 0 in.	432
4ft. 0 in. by   4ft. 0 in.	50	11 ft. 6 in. by 14 ft. 0 in.	504
4 ft. 0 in. by   6 ft. 0 in.	75	11 ft. 6 in. by 16 ft. 0 in.	576
6 ft. 0 in. by   4 ft. 0 in.	70	11 ft. 6 in. by 18 ft. 0 in.	648
6 ft. 0 in. by   6 ft. 0 in.	105	11 ft. 6 in. by 20 ft. 0 in.	720
6 ft. 0 in. by   8 ft. 0 in.	140	14 ft. 0 in. by 14 ft. 0 in.	616
6 ft. 0 in. by 10 ft. 0 in.	175	14ft. Oin. by 16 ft. 0 in.	704
6 ft. 0 in. by 12 ft. 0 in.	210	14 ft. 0 in. by 18 ft. 0 in.	792
8 ft. 0 in. by   6 ft. 0 in.	150	14 ft. 0 in. by 20 ft. 0 in.	880
8 ft. 0 in. by   8 ft. 0 in.	200	14 ft. 0 in. by 24 ft. 0 in.	1,056
Capacity per Square Foot of Filtering Area.—Accoring to the Oliver Co. the dry solids of various kinds which can be obtained from a square foot of surface are: For sulphate of lime in phenol manufacture, 750 lb.; 200 Ib. of molasses in cold saccharate work, l,5001b. of molasses in hot work, 3,500 of bicarbonate of soda, lime mud in caustic extraction, 750 lb. per 24 hours.
On cement slurry, ores and flotation concentrates the capacity will range from 200 to 1,300 Ib. per 24 hr. per square foot of filter surface. Many plants will run under the smaller of these two figures through overestimation of the size of filter required, irregularities of operating, etc. Where the lower figure is reached with steady operation and giving the filter all the material it will handle and thickened as much as possible the limits of vacuum filtration for the substances mentioned have been